# How can one use the earth as a second wire?

I read recently that the earth can be used as a wire to save wiring costs. My understanding of how this works is that a power source, say a battery, separates charge, creating electrons on one side and the absence of electrons on the other, or negative and positive voltage. So a 3V battery would produce -1.5V and 1.5V. Then if we hooked either side of this battery to a ground which has 0V, electrons would flow from the -1.5V to the ground and from the ground to the 1.5V.

However if this were true it seems that if we put a resistor on either side of the battery it would only enjoy half the voltage, i.e 1.5V, that the battery an produce since that is the difference between either side of the battery terminal and ground.

Thus Single Wire Earth Return solutions sacrifice 50% voltage for saving 50% wire cost. However, I cannot find any information stating my analysis is true. Thus I suspect there's something wrong with my reasoning and understanding of electricity.

Thanks for the help!

• Your 50/50% assumes that both resistances are the same; do some calculation for actual real restistances and you will find out for that real case. – PlasmaHH Nov 25 '15 at 13:22
• There is no absolute voltage reference; a 3v battery has its positive terminal 3v higher than its negative terminal, not 1.5v either side of some sort of universal ground voltage. – Nick Johnson Nov 25 '15 at 13:22
• So if you were to connect both sides of the terminal to the ground would the difference between one terminal and the ground be 3V? If so how does the ground become the same voltage relative to one terminal as the other terminal? – Bowen Jin Nov 26 '15 at 15:10

## 1 Answer

Your assumption is based on the fact that all voltages are referred to a "common" ground. But that's not true!

The voltage is also called "electric potential difference"; note the word "difference".

This means that a "3V voltage" means nothing; you should specify with respect to what. In your case a "3V voltage" battery is a battery whose + terminal has an electric potential 3V higher than its - terminal. If you try to measure the voltage between either of its terminals and the ground, without making any connections, you will always read 0V.

That's why you can put batteries in series to get a higher voltage.

• If the voltage difference between either of the terminals and the ground is always 0V how can there be current flow through the ground? – Bowen Jin Nov 25 '15 at 19:58
• Exactly, there CAN'T be any current flow if you just connect ONE terminal. But as soon as you connect BOTH terminals you will have a current flow. But you have to connect BOTH terminals, not just one. Anyway it's really easy to test: just use a multimeter – frarugi87 Nov 26 '15 at 9:41
• When you connect both sides how does the current flow. Does the positive terminal take electrons from the ground and the negative side gives electrons like I said? If that's the case if one were to put a resistor in between the terminal on either side and the ground what would be the voltage difference across the resistor? – Bowen Jin Nov 26 '15 at 15:05